Methods of rolling strip materials, and strip materials rolled thereby

ABSTRACT

For initial threading of a coil of metal through a rolling mill the settings of the mill are modified, in accordance with calculated and measured data, to minimize the amount of distortion on the nose of the coil of metal. The settings of the mill are then returned to a nominal schedule for rolling the rest of the coil.

United States Patent [1 1 Beeston et al.

[ June 24, 1975 METHODS OF ROLLING STRIP MATERIALS, AND STRIP MATERIALS ROLLED THEREBY Inventors: John Wilmot Beeston, Rugby;

Greyham Frank Bryant, Southall; Peter David Spooner, Pinner, all of England Assignee: Gee-Elliott Automation Limited,

Hertfordshire, England Filed: Aug. 19, 1974 Appl. No.: 498,549

Foreign Application Priority Data Aug. 23, 1973 United Kingdom 40000/73 U.S. Cl. 72/6 Int. Cl B2lb 37/00 Field of Search 72/8, 10, ll, l6, l9, 6

[5 6] References Cited UNITED STATES PATENTS 3,248,916 5/1966 Kenyon et al 72/16 X 3,253,438 5/1966. Stringer 72/12 3,387,470 6/1968 Smith, Jr 72/7 3,813,908 6/1974 Miglore 72/21 3,820,71 l 6/ 1974 Economopoulos et al. 72/7 Primary Examiner-Milton S. Mehr Attorney, Agent, or Firml(irschstein, Kirschstein, Ottinger & Frank [5 7] ABSTRACT For initial threading of a coil of metal through a rolling mill the settings of the mill are modified, in accordance with calculated and measured data, to minimize the amount of distortion on the nose of the coil of metal. The settings of the mill are then returned to a nominal schedule for rolling the rest of the coil.

2 Claims, 2 Drawing Figures Thread Roll Force Calculzllor lol l ()omparalor Mill Thermal Crown Calculalor Dala Roll

Zero Sha Force Czfillalo lOA Jack Force Gauge Change Caloulalor Oulpul Programmer Flgjs rower strips.

1 METHODS OF ROLLING STRIP MATERIALS, AND STRIP MATERIALS ROLLED THEREBY This invention relates to methods of rolling strip material, and more particularly but not exclusively,- to rolling of metal strip, such aslsteel strip, and also to strip material rolled by these methods. K

It is well known thatin the rolling of steel strip, particularly broad thin strip, care must be exercised to avoid what is known as bad shape. Shape refers to the transverse cross-section of the strip i.e. transverse gauge profile, and transverse variation in the longitudinal tension/stress pattern of the strip.'Excessive stress differences across the strip can cause buckling of the strip, i.e. manifest bad shape. If the strip is subjected to sufficient longitudinal tension, buckling may" be avoided but the potential for buckling is not necessarily eliminated, in which case the strip has Iaterit'bad shape, and may buckle for example when cut into nar- When threading strip into a mill, particularly a multistand tandem mill, for subsequent rolling to reduce gauge, the shape of the nose i.e. the first few-feet of the strip can give rise to great difficulties of threading, particularly as tension cannot be applied to obviate manifest bad shape. In some cases, bad nose shape may prevent the nose enteringa stand v(or automatic threading devices for a stand, where employed). The operator then has to stop the mill, cut off the bad nose, and reattempt threading. This results in undesirable scrap, and loss of mill utilisation time.

It is therefore an object of the invention to provide a method .of rolling strip materialswhich obviates: or mitigates the above difficulties of threading.

According ,to one aspect of the invention a method of rolling strip material in a rolling mill havingat least one adjustable rolling stand, comprises the steps of:

a. from measurements of the mill settingsand. data regarding the strip material to be rolled, calculating at least approximately the roll force to give the required gauge which should theoretically occur on the nose of the strip material at each stand, and also calculating theoretically the roll camber at each stand;

b. determining at least approximately the ideal roll force for each stand which, with the calculated roll camber on the respective stand, will give the nose a shape threadable into a subsequent rolling stand or a shape within predetermined limits of badness;

c. comparing the calculated roll force at each'stand withthe determined ideal roll force 'at that respective stand, and if the calculated roll force differs from the determined ideal roll force sufficiently to give thenose an unthreadable shape or a shape; outsidepredetermined limits of badness, modifying the mill settings to produce a roll force and/or a roll camber for each stand which will give the nose a threadable shape or a shape within predetermined limits of badness;

threading the strip material through the mill and as, each inner-stand tension is successively" established,

changing the settings of the mill tothose settings appropriate to a predetermined rolling schedulejiif not al A rolling mill having at least one adjustable rolling, 7

stand, including a. means for sequentially measuring the mill settings and data regarding the strip material to be rolled, means for calculating at least approximately the roll force to give the required gauge which should theoretically occur on the nose of the strip materialat ,each stand, and also means for calculating theoretically the roll camber at each stand;

b. means for determining at least approximately the ideal roll force for each stand which, with the calculated roll camber on the respective stand, will give the nosea shape threadable into a subsequent rolling stand or a shape within predetermined limits of badness;

c. means for comparing the calculated roll force at each stand with the determined ideal roll force at that respective stand, and if the calculated roll force differs from the determined ideal roll force sufficiently to give the'nose an unthreadable shape or a shape outside predetermined limits of badness, means for modifying the mill settings to produce a roll force and/or a roll camber for each stand which will give the nose a threadable shape or a shape within predetermined limits of badness;

(1. means for threading the strip material through the mill and as each inter-stand tension'is successively established, changing the settings of the mill to those settings appropriate to a predetermined rolling schedule (if not already at those settings); and

e. means for rolling the strip material substantially according to the rolling schedule.

lnterstand-tension includes the tension between the final standand the reel. i

The mill settings which may be modified in step (0) may be roll gap, and alternatively or additionally in the case where there is provision for varying roll camber, (for example by roll-bending jacks), roll camber.

The roll camber calculation of step (a) may be based on a knowledge of camber built-in to the rolls of the rolling stand in question, for example by grinding dur-- ing their manufacture and roll wear during use, together with a knowledge of thermal dissipation in the rolls during working and idling periods which when applied to a mathematical model of the dynamic thermal camber of therolls, gives the instantaneous thermal camber. 1 L V i The aforesaid calculations'may be performed in a computer, preferably a suitably programmed digital computer.v

Another aspect of the present invention comprises strip material when rolled by the above method. In a preferred embodiment said rolled strip material may b for example steel or aluminium.

Embodiments of the invention will now be described by way of example, with reference to the problems of threading a coil of steel stripinto a multi-stand cold rolling tandem mill and with reference to FIGS. 1 and 2 of the drawings. U

The resultant shape of the coil nose after threading through a roll stand is dependent on how. close is the roll force which occurs in rolling thenosecompared with the roll force which will deform the work rolls (by bending and flattening) so as to compensate for the total camber (ground and thermal) existing on the rolls. If compensation is correct then the shape of the rolls will exactly match the incoming transverse gauge profile of the strip and perfect exit shape results. If

, compensation is not exact then the shape of the rolls,

as the nose is being rolled, will not match the incoming transverse gauge profile and various degrees of bad shape occur. There are two possibilities alter the total crown of the rolls by some additional means of roll bending e.g. jacks or alter the roll force which will occur during rolling of the nose. For a stand without roll bending jacks there is only the latter possibility.

The description now refers, by way of example to a four-stand tandem mill with roll bending jacks on the first and last stand.

The steps involved in the method for ensuring good shape on the nose are as follows:

a. The roll force which will theoretically occur on the nose i.e. the front first few feet of the strip is calculated using known models giving roll force F as a function of inter-stand thickness during threading of the strip, inter-stand tensions, yield stress of the strip and roll gap friction.

Such a model gives the following dependence F Wf (h T", K", n) for stand 1' where F total roll force W width of strip being rolled by threading gauges on thickness of strip T inter-stand tension K Yield stress of the strip ,1. friction in roll gap at stand i f indicates that F is a function of the above variables.

The roll camber is also calculated as follows:

The ground camber is known for each stand from the dimensions of the rolls. The thermal camber, to be added to the effect of the ground camber is then calculated as follows:

Firstly when pre-calculating the set up for a coil a coefficient of thermal camber per unit speed Ci is calculated for each stand. The equation for this is based on the proportion of the losses in each roll gap that flow into the rolls. This causes differential thermal expansion and changes in the camber of the rolls.

The thermal camber coefficient for stand i is calculated assuming that the rolls had settled down to steady state conditions i.e. as if the coil had been rolled at one per unit speed for an infinite time. 7

The formula for Ci is as follows:

K In (1-H) 5 where K exit yield stress from stand i Hrc r reduction from thickness at the exit stand i i.e. the amount of reduction of thickness from mill entry to the exit of stand i.

Secondly estimates of thermal camber C (t) are calculated every 15 secs as follows:

I. A single measurement of the stand speed w,- is

taken for each of the stands.

2. The steady state camber at time t is calculated 0.." r w. 0' i 1,2,3,4

Where C is the steady state camber/unit speed as calculated above and C... (t) is the thermal camber that would be reached running at speed (o for an infinite time.

3. The actual Thermal camber C (t) at time t is therefore given by: C "(t) l, C "(t) l C r-Az) 1 C"(z2A z) l Cm"(z-At) l Cm(- t-ZAt) i l C (t-3At) 4. All values of C and C, are updated'by shifting one value in time every 15 secs.

Thus C J(t) is calculated from present and previous values of the steady state camber e.g. Cm"(t) and from previous values of the actual thermal camber i.e. Cm t-At) where A z the sampling interval of 15 secs, and l l 1 are constants.

b. Having now obtained the calculated roll camber the ideal roll force can be calculated as follows:

The zero shape roll force per unit strip width is given by:

Cu, is the work roll camber estimate, fi etc are constants, GC is the ground camber at st and i; Wf is the roll face width.h is the entry gauge to the mill The ideal roll forces are thus given by F.) S'W W= strip width) I c. The tolerances F on ideal shape is F =f (l f W+f, h i l to 4. fi are constants. The inequality (Rf-F 5 F 5 (F +F is tested for stands 1 to 4 in succession.

Therefore no changes are made unless this limit is exceeded. If the limit is exceeded then a minimum change P11 is made to the roll force at each stand to return to within the required limits. This minimum change then leaves the roll force as near as possible to that which will give the desired gauge and therefore causes a minimum change in gauge.

If this limit is exceeded on any of the stands then, defining the threading gauge offsets to compensate for bad shape during threading are specified by the equations I dh i There are upper and lower limits to Ah as follows:

Ah =f if Ah f Ah =f,-, if Ah f Ah O (for the first stand i.e. the entry gauge to the mill) Ahi change on stand i for shape only h exit gauge from stand i (dP/dh), change of roll force with exit gauge at stand i f .,f are constants AFli is mathematically defined above and is the change in gauge force which will be made to obtain tolerable shape Mi mill modulus hi-l is entry gauge to stand i Ah total thread gauge change of previous stand Ah is the total thread gauge change for stand i and is in two parts (i) the change for shape only Ah (ii) the effect of Ah The mill settings for the stands of the mill can then be recalculated from the roll forces F, AF, and the gauges k h,--Ah

The first and last stands have roll bending jacks and the required jack forces Ji (for stand i) are given by KO KO are constants determined by the mill geometry.

These changes are made to the various stands and the mill is then ready to receive the strip.

(1. The change of settings (e.g. screw positions for rolls, roll speeds, jack forces) to return to the settings appropriate to a predetermined rolling schedule are accomplished by removing the changes made at each stand in sequence as the strip enters the following stand. This then minimises the amount of off-gauge material produced.

The change of settings is preferably accomplished without disturbing interstand tensions, for example by employing the non-interactive gauge control methods described in Journal of The Iron and Steel Institute, Volume 209, part 11, November 1971, pages 869 to 875.

Referring now to FIG. 1 which shows the implementation of this invention in a digital computer 22 (see FIG. 2) block 100 is the predetermined rolling schedule (i.e. interstand gauges and tensions. This could, for example, be obtained from punched paper tape or calculated by a computer programme. This schedule is fed as input to a thread rollforce calculator block 101 in which the rollforce which will theoretically occur on the nose is calculated in accordance with section (a) of the above described method.

The nominal schedule from is also fed to a thermal camber calculator 102 which calculates the thermal camber'as described in section (a) above to be used by the zero shape rollforce calculator 103 as described in section (b) above.

The outputs of 101 and 103 are compared in comparator 104 as described in section (0) above and the output'of 104 is used to calculate the jack force settings and gauge changes required for threading as described in section (0) above. The output programme is then used to apply these settings to mill during threading and remove them as described in section (d) above.

FIG. 2 shows a rolling mill with 4 stands 1 to 4, metal strips to be rolled, screws position controllers 5 to 8, speed controllers 9 to 12 and jack force controllers 13, 14. The digital computer, 22, as described with reference to FIG. 1, calculates the jack forces 1,, .l and thread gauge corrections Ah which are applied to the controllers through the gain setting amplifiers 15 to 21, and summing amplifiers 23, 24.

Alternatively if the mill is equipped with automatic tension controls using the screwdowns at each stand then this can be used to remove the threading changes as the strip passes through the mill.

If the mill has no roll bending jacks then it is difficult to achieve both the correct gauge and shape for the nose of the coil. However with roll bending jacks by adjusting both the roll gap and the jack force it is much easier to obtain both correct gauge and shape.

What we claim is:

1. A method of rolling strip material in a rolling mill having at least one adjustable rolling stand, comprises the steps of:

a. from measurements of the mill settings and data regarding the strip material to be rolled, calculating at least approximately the roll force to give the required gauge which should theoretically occur on the nose of the strip material at each stand, and also calculating theoretically the roll camber at each stand;

b. determining at least approximately the ideal roll force for each stand which, with the calculated roll camber on the respective stand, will give the nose a shape threadable into a subsequent rolling stand or a shape within predetermined limits of badness;

c. comparing the calculated roll force at each stand with the determined ideal roll force at that respective stand, and if the calculated roll force differs from the determined ideal roll force sufficiently to give the nose an unthreadable shape or a shape outside predetermined limits of badness, modifying the mill settings to produce a roll force and/or a roll camber for each stand which will give the nose a threadable shape or a shape within predetermined limits of badness;

. threading the strip material through the mill and as each inter-stand tension is successively established, changing the settings of the mill to those settings appropriate to a predetermined rolling schedule (if not already at those settings); and

e. rolling the strip material substantially according to the rolling schedule.

3,890,817 7 8 2. A rolling mill having at least one adjustable rolling that respective stand, and if the calculated roll stand, including force differs from the determined ideal roll force a. means for sequentially measuring the mill settings ffl i ml t i e th no e an unthreadable shape and data regarding the strip material to be rolled,

or a shape outside predetermined limits of badness,

gil go rig2:2 :2 is:lief;i fe g gzggg vtilfiii go3;; 5 means for modifying the mill settings to produce a roll force and/or a roll camber for each stand which theoretically occur on the nose ofthe strip material will give the nose 8 threadable Shape or a shape fifii iil roll 3511 83 2? lilifi siill Within p'edete'mined t bad'tess;

b. means for determining at least approximately the 10 means far threacimg the smp l f" through the ideal r0 force for each Stand which with the mill and as each inter-stand tension is successively culated roll camber on the respective stand, will establishefj changing the Settings of mm to give the nose a shape threadable into a subsequent Phose Settmgs ppropnate to a predetemlmed roll rolling stand or a shape within predetermined limits mg Schedule (If not already at those settmgs); and f b d l5 means for rolling the strip material substantially 0. means for comparing the calculated roll force at according to the rolling schedule. each stand with the determined ideal roll force at 

1. A method of rolling strip material in a rolling mill having at least one adjustable rolling stand, comprises the steps of: a. from measurements of the mill settings and data regarding the strip material to be rolled, calculating at least approximately the roll force to give the required gauge which should theoretically occur on the nose of the strip material at each stand, and also calculating theoretically the roll camber at each stand; b. determining at least approximately the ideal roll force for each stand which, with the calculated roll camber on the respective stand, will give the nose a shape threadable into a subsequent rolling stand or a shape within predetermined limits of badness; c. comparing the calculated roll force at each stand with the determined ideal roll force at that respective stand, and if the calculated roll force differs from the determined ideal roll force sufficiently to give the nose an unthreadable shape or a shape outside predetermined limits of badness, modifying the mill settings to produce a roll force and/or a roll camber for each stand which will give the nose a threadable shape or a shape within predetermined limits of badness; d. threading the strip material through the mill and as each inter-stand tension is successively established, changing the settings of the mill to those settings appropriate to a predetermined rolling schedule (if not already at those settings); and e. rolling the strip material substantially according to the rolling schedule.
 2. A rolling mill having at least one adjustable rolling stand, including a. means for sequentially measuring the mill settings and data regarding the strip material to be rolled, means for calculating at least approximately the roll force to give the required gauge which should theoretically occur on the nose of the strip material at each stand, and also means for calculating theoretically the roll camber at each stand; b. means for determining at least approximately the ideal roll force for each stand which, with the calculated roll camber on the respective stand, will give the nose a shape threadable into a subsequent rolling stand or a shape within predetermined limits of badness; c. means for comparing the calculated roll force at each stand with the determined ideal roll force at that respective stand, and if the calculated roll force differs from the determined ideal roll force sufficiently to give the nose an unthreadable shape or a shape outside predetermined limits of badness, means for modifying the mill settings to produce a roll force and/or a roll camber for each stand which will give the nose a threadable shape or a shape within predetermined limits of badness; d. means for threading the strip material through the mill and as each inter-stand tension is successively established, changing the settings of the mill to those settings appropriate to a predetermined rolling schedule (if not already at those settings); and e. means for rolling the strip material substantially according to the rolling schedule. 